Extensible ladder

ABSTRACT

An extensible ladder includes a plurality of sections, each having a pair of tubular uprights connected by a rung, with the uprights of each section being slidably engaged with the corresponding uprights of an adjacent section. The inside surface of the tubular uprights are provided with longitudinally extending grooves, which reduce the area of sliding contact between adjacent uprights, thereby making the ladder easier to extend or collapse.

This invention relates to an extensible ladder.

Various types of extensible ladder have been proposed hitherto. U.S.Pat. No. 1,712,942 discloses one such ladder comprising a plurality ofsections each having a pair of tubular uprights connected at their upperends by a rung, with the tubular uprights of each section being asliding fit with the corresponding uprights of the adjacent sections.

The adjacent uprights need to be a tight fit with each other, so thatthe ladder is rigid when it is erected. However, this tight fit makesthe ladder extremely difficult to extend and collapse. The sliding areasof contact between adjacent upright sections wear with prolonged use,and thus the ladder becomes increasingly less rigid. Any dust or swarfthat gets trapped between the uprights will cause the ladder to jam whenit is being collapsed or extended.

We have now devised an extensible ladder which alleviates theabove-mentioned problems.

In accordance with this invention there is provided an extensible laddercomprising a plurality of sections, each section having a pair ofuprights connected by a rung, with the uprights of each section beingslidably engaged with the corresponding uprights of an adjacent section,the uprights being formed with longitudinally extending grooves whichreduce the area of sliding contact between adjacent uprights.

The friction between adjacent uprights is greatly reduced owing to thegrooves reducing the area of sliding contact between them. This makesthe ladder very much easier to extend or collapse than conventionalextensible ladders. The areas of sliding contact between adjacentuprights do not wear as badly as conventional extensible ladders, andthus the ladder does not suffer from the problems of poor rigidity. Anydust or other particles that get caught between the uprights willcollect in the grooves rather than between the areas of sliding contact.The ladder is thus less prone to jamming.

Preferably the uprights are tubular or channel-section, the groovesbeing formed on the inside surfaces of the uprights, so that they arehidden from view.

It is known to apply oil or other liquid lubricants to the uprights ofextensible ladders to reduce the sliding friction, thereby making theladder easier to extend and collapse. This lubrication is messy, sinceit gets on the hands and clothes of persons climbing the ladder.Furthermore, in time the lubrication becomes discoloured, and thusstains any objects which come into contact with the ladder.

Thus, preferably a dry friction-reducing coating, such aspolytetrafluoroethylene (PTFE), is applied to the areas of slidingcontact of the uprights of the ladder sections.

Preferably the sections of the ladder can be separated from each other,so that they can be cleaned, and so that damaged sections can bereplaced.

When a person climbs a ladder, a considerable amount of downwards forceis applied to the rungs. Thus, the rungs need to be securely attached tothe uprights. Generally in conventional non-extensible ladders, therungs extend through tubular uprights so as to form a rigid connectiontherebetween. It is not possible to construct extensible ladders in thisway, since the rungs would obstruct the sliding action of the uprights.Preferably the rungs are therefore attached to the outside of thetubular uprights by welding. Some materials, particularly aluminium, arenot easy to weld whilst maintaining necessary tolerances. It will beappreciated that the tolerances involved in constructing extensibleladders are critical, for example if the distance between the oppositeuprights of each section is not exactly correct, then the sections ofthe ladder will not fit together properly. However, these accuratetolerances can be achieved using jigs and robotic welding apparatus.

The rungs of U.S. Pat. No. 1,712,942 are welded to the uprights, and itwill be appreciated that the welds need to penetrate into respectiveareas of the uprights and rungs, so that a strong connection is formedtherebetween. A disadvantage of weld penetration is that distortion orover penetration occurs inside the uprights, which interferes with thesliding action of the ladder.

We have found that the grooves serve to accommodate a large proportionof any distortion caused by weld penetration.

However, preferably the rungs are welded to the uprights at points onthe outside surfaces of the uprights which correspond to the grooves onthe inside surface of the uprights. Thus, any distortion or overpenetration which occurs in the uprights will be confined to thegrooves, and thus will not interfere with the sliding action of theladder

Preferably the rungs and uprights are cut from extrusions of e.g.aluminium. Preferably the rungs are tubular.

Preferably the rungs are mounted such that at least the front edgethereof is spaced from the end of the uprights from which the adjacentsection slides, the rung of the adjacent section resting against saidend of the uprights when the ladder is collapsed. Thus, when the ladderis collapsed, the user avoids trapping his fingers between the adjacentuprights, because the front edge of the rung is spaced from the end ofthe uprights.

An embodiment of this invention will now be described by way of exampleonly and with reference to the accompanying drawings, in which:

FIG. 1 is a front view of an extensible ladder in accordance with thisinvention, when the ladder is collapsed;

FIG. 2 is a perspective rear view of the ladder of FIG. 1, when theladder is collapsed;

FIG. 3 is a side view of the ladder of FIG. 1, when the ladder iscollapsed;

FIG. 4 is a perspective view of the ladder of FIG. 1, when the ladder isextended;

FIG. 5 is a sectional view along the line V--V of FIG. 1;

FIG. 6 is a longitudinal sectional view through a rung of the ladder ofFIG. 1; and

FIG. 7 is a sectional view along the line VII--VII of FIG. 4.

Referring to FIGS. 1 to 4 of the drawings, there is shown an extensibleladder which is formed from extruded aluminium components and is lightin weight. The ladder comprises a plurality of sections A-n which aretelescopically engaged with each other. Each section comprises a pair oftubular uprights 10, which are generally rectangular in cross-section,and which are interconnected at their upper ends by a tubular rung 11.

Referring to FIG. 5 of the drawings, the uprights 10 of each sectionhave longitudinally extending grooves 13 formed on their insidesurfaces, and defining ribs 14 between the grooves 13. The uprights 10of each section of the ladder engage, as a close but sliding fit, intothe uprights of the ladder section below. The front edge of the rung 11of each section is spaced from the top of the upright of that section,such that the rung 11 slopes upwardly from front to back when the ladderis vertical. The uprights 10 of each section are all the same height aseach other, but are progressively smaller in cross-section towards thetop section. When the ladder is extended, the rungs 11 are all an equaldistance apart from each other.

In extending or collapsing the ladder, the ribs 14 form the area ofsliding contact between adjacent uprights. A layer (not shown) of hardwearing friction-reducing material is disposed over the outside of eachof the uprights, so as to reduce the friction between the slidingaluminium uprights. The material is preferably of a type which transfersonto areas which come into contact with the layer.

Front and rear walls of each upright 10 are convex, and are arranged tocontact the corresponding upright of the ladder section below at theirradially outermost part only. Thus, longitudinally extending spaces 15are formed between the corners of the adjacent uprights. These areas ofcontact on the front and rear walls are also coated with theabove-mentioned friction-reducing material.

The uppermost section comprises uprights 10n which are formed with alongitudinally extending channel 16 on their front and rear walls, whichserve to strengthen the uppermost section.

Referring to FIG. 6 of the drawings, when the ladder is extended,spring-loaded circular-section metal bolts 20 in the rungs 11 engagewithin apertures 21 formed towards the lower end of the inner walls ofthe uprights of the ladder section above. Thus, in order to extend theladder, the top ladder section is pulled out until the spring-loadedbolts 20 of the ladder section below spring into its locking apertures21, then the next section is pulled out, and so on. Preferably the bolts20 are coated with a layer of hard wearing friction-reducing material.

In order to collapse the ladder, the bolts 20 of the top ladder sectionare retracted, so that its uprights 10n can drop into the uprights ofthe ladder section below, then the bolts of that section are retractedand so on. In order to retract the bolts 20 of each ladder section, eachbolt 20 is provided with a plastics release catch 22, which projectsdownwardly from the underside of the rung 11.

As shown in FIG. 7, each rung e.g. 11c comprises a tubularrectangular-section extrusion having a channel-section longitudinallyextending slot 24 on its underside. The locking bolts 20 are slidablymounted in a substantially circular-section portion at the base of theslot 24. A helical spring 23, also disposed in the base of the slot 24,acts between the bolts 20 so as to bias them outwardly from respectiveopposite ends of the rung 11c.

The plastics release catches 22 are connected to respective bolts 20 bymeans of an elongate arm 25 which extends longitudinally along the neckof the slot 24. The outer end of each arm 25 comprises a C-shaped clip26, which engages with a peripheral groove 27 formed on the inner end ofthe bolt 20. Three flat plastics covering strips 28 snap-engage into arecess formed in the opening of the slot 24 on each rung, so as toconceal the bolt and catch mechanism inside.

The uprights 10A of the lowermost section are interconnected at theirlower ends by an extra rung 31. Each of the rungs 11A-11n, 31 areattached to the uprights by welds. The uppermost rung 11n projectsoutwardly from the uprights 10n, and in use forms a stabiliser whichrests against a wall or other flat structure. Opposite ends of theuppermost rung 11n are provided with rubber end-caps 32. The foot of theladder is also provided with rubber feet 33.

Each rung 11 is welded to respective uprights 10 along its front andrear faces only, as denoted by W in FIGS. 3 and 5. The welds connect therungs 11 to the outside surfaces of the uprights 10 at points whichcorrespond to the longitudinally extending spaces 15 on their insidesurfaces. Thus, any distortion caused by weld penetration will beconfined to the longitudinally extending spaces 15, and will thus notinterfere with the sliding action of the ladder.

In use, when the ladder is stood against a wall or other structure, theinclined upper surface of the rungs 11 assume a horizontal position. Theladder does not bend excessively when it is climbed, owing to the tightfit between adjacent uprights of the ladder sections. However, thefriction-reducing coating prevents this tight fit between the uprightsfrom making the ladder difficult to extend and collapse.

It will be appreciated that the ladder is particularly compact when itis collapsed, yet it can be extended very quickly and easily to form aversatile rigid ladder.

I claim:
 1. An extensible ladder comprising a plurality of sections,each section having a pair of tubular uprights which comprisesubstantially flat parallel side walls and convex front and rear walls,the side walls of the respective uprights of each section beingconnected by a rung, with the uprights of each section beingtelescopically engaged with the corresponding uprights of an adjacentsection, the uprights being formed with longitudinally extending grooveswhich reduce the area of sliding contact between adjacent sections. 2.An extensible ladder as claimed in claim 1, in which the front and rearwalls of each upright contact the corresponding uprights of adjacentsections at their radially outermost part only.
 3. An extensible ladderas claimed in claim 2, in which longitudinally extending spaces areformed between corners of the adjacent uprights.
 4. An extensible ladderas claimed claim 1, in which the grooves are formed on the insidesurfaces of the uprights.
 5. An extensible ladder as claimed claim 1, inwhich the rungs are welded to the uprights.
 6. An extensible ladder asclaimed claim 1, in which the uprights and rungs are formed fromaluminium.
 7. An extensible ladder as claimed in claim 6, in which theuprights and rungs are cut from extrusions of aluminium.
 8. Anextensible ladder as claimed claim 1, in which a dry friction-reducingcoating is applied to areas of sliding contact of the uprights of theladder sections.
 9. An extensible ladder as claimed in claim 8, in whichthe coating comprises polytetrafluoroethylene (PTFE).
 10. An extensibleladder as claimed claim 1, in which the sections of the ladder areseparable from adjacent sections.
 11. An extensible ladder as claimedclaim 1, in which the rungs are mounted such that at least the frontedge thereof is spaced from the end of the uprights from which theadjacent section slides, the rung of the adjacent section restingagainst said end of the uprights when the ladder is collapsed.